Method of controlling photolithography processes based upon scatterometric measurements of sub-nominal grating structures

• US 6,582,863 B1
• Filed: 06/11/2001
• Issued: 06/24/2003
• Est. Priority Date: 06/11/2001
• Status: Active Grant

• Current Assignee: Advanced Micro Devices, Inc.
• Original Assignee: Advanced Micro Devices, Inc.
• Inventors: Stirton, James Broc, Lensing, Kevin R.
• Primary Examiner(s): Young, Christopher G.
• Application Number:
  US09/879,751
• Time in Patent Office: 743 Days
• Field of Search: 430/30
• US Class Current: 430/30
• CPC Class Codes: G03F 7/70616 Monitoring the printed patterns
• CPC Class Codes: G03F 7/7065 Defects, e.g. optical inspection of patterned layer for defects

Abstract

The present invention is generally directed to a method of controlling photolithography processes based upon scatterometric measurements of sub-nominal grating structures, and a system for accomplishing same. In one embodiment, the method comprises providing a library of optical characteristic traces, each of which corresponds to a sub-nominal grating structure comprised of a plurality of photoresist features having a known degree of residual photoresist material positioned between the photoresist features, forming a process layer above a semiconducting substrate, and forming a layer of photoresist above the process layer. The method further comprises forming at least one sub-nominal grating structure in the layer of photoresist, the sub-nominal grating structure being comprised of a plurality of photoresist features, illuminating the formed sub-nominal grating structure, measuring light reflected off of the formed sub-nominal grating structure to generate an optical characteristic trace for the formed sub-nominal grating structure, and determining the presence of residual photoresist material between the features of the formed sub-nominal grating structure by comparing the generated optical characteristic trace to at least one optical characteristic trace from the library.

Claims

1. A method, comprising:

providing a library of optical characteristic traces, each of which corresponds to a sub-nominal grating structure comprised of a plurality of photoresist features having a known degree of residual photoresist material positioned between said photoresist features;

forming a process layer above a semiconducting substrate;

forming a layer of photoresist above said process layer;

forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features;

illuminating said formed sub-nominal grating structure;

measuring light reflected off of said formed sub-nominal grating structure to generate an optical characteristic trace for said formed sub-nominal grating structure; and

determining the presence of residual photoresist material between said features of said formed sub-nominal grating structure by comparing said generated optical characteristic trace to at least one optical characteristic trace from said library.

2. The method of claim 1, further comprising modifying at least one parameter of a photolithography process used to form a patterned layer of photoresist on at least one subsequently processed wafer based upon said determined presence of residual photoresist material between said photoresist features of said sub-nominal grating structure.

3. The method of claim 1, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming a plurality of sub-nominal grating structures in said layer of photoresist.

4. The method of claim 2, wherein modifying at least one parameter of a photolithography process used to form a patterned layer of photoresist on at least one subsequently processed wafer comprises modifying at least one of a stepper exposure dose, a stepper focus, and a duration of a photoresist development process.

5. The method of claim 1, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming at least one sub-nominal grating structure in said layer of photoresist above a scribe line of said wafer.

6. The method of claim 1, wherein said photoresist features comprising said formed sub-nominal grating structure are comprised of lines or trenches.

7. The method of claim 1, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a critical dimension that is less than a critical dimension of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

8. The method of claim 1, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a spacing that is less than a spacing of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

9. The method of claim 1, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a critical dimension and a spacing that is less than a critical dimension and a spacing of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

10. The method of claim 1, wherein forming a process layer comprises forming a process layer comprised of at least one of a metal, polysilicon and an insulating material having a dielectric constant less than 5.0.

11. The method of claim 1, wherein forming a layer of photoresist above said process layer comprises forming a layer of positive or negative photoresist above said process layer.

12. A method, comprising:

providing a library of optical characteristic traces, each of which corresponds to a sub-nominal grating structure comprised of a plurality of photoresist features having a known degree of residual photoresist material positioned between said photoresist features;

forming a process layer above a semiconducting substrate, said process layer comprised of at least one of a metal, polysilicon, and a material having a dielectric constant less than 5.0;

forming a layer of photoresist above said process layer;

forming at least one sub-nominal grating structure in said layer of photoresist above a scribe line of a wafer, said sub-nominal grating structure being comprised of a plurality of photoresist features;

illuminating said formed sub-nominal grating structure;

measuring light reflected off of said formed sub-nominal grating structure to generate an optical characteristic trace for said formed sub-nominal grating structure;

determining the presence of residual photoresist material between said features of said formed sub-nominal grating structure by comparing said generated optical characteristic trace to at least one optical characteristic trace from said library; and

modifying at least one parameter of a photolithography process used to form a patterned layer of photoresist on at least one subsequently processed wafer based upon said determined presence of residual photoresist material between said photoresist features of said sub-nominal grating structure.

13. The method of claim 12, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming a plurality of sub-nominal grating structures in said layer of photoresist.

14. The method of claim 12, wherein modifying at least one parameter of a photolithography process used to form a patterned layer of photoresist on at least one subsequently processed wafer comprises modifying at least one of a stepper exposure dose, a stepper focus, and a duration of a photoresist development process.

15. The method of claim 12, wherein said photoresist features comprising said formed sub-nominal grating structure are comprised of lines or trenches.

16. The method of claim 12, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a critical dimension that is less than a critical dimension of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

17. The method of claim 12, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a spacing that is less than a spacing of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

18. The method of claim 12, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a critical dimension and a spacing that is less than a critical dimension and a spacing of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

19. The method of claim 12, wherein forming a layer of photoresist above said process layer comprises forming a layer of positive or negative photoresist above said process layer.

20. A method, comprising:

providing a library of optical characteristic traces, each of which corresponds to a sub-nominal grating structure comprised of a plurality of photoresist features having a known degree of residual photoresist material positioned between said photoresist features;

forming a process layer above a semiconducting substrate;

forming a layer of photoresist above said process layer;

forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features that have a critical dimension that is less than a critical dimension of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device;

illuminating said formed sub-nominal grating structure;

measuring light reflected off of said formed sub-nominal grating structure to generate an optical characteristic trace for said formed sub-nominal grating structure;

determining the presence of residual photoresist material between said features of said formed sub-nominal grating structure by comparing said generated optical characteristic trace to at least one optical characteristic trace from said library; and

modifying at least one parameter of a photolithography process used to form a patterned layer of photoresist on at least one subsequently processed wafer based upon said determined presence of residual photoresist material between said photoresist features of said sub-nominal grating structure.

21. The method of claim 20, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming a plurality of sub-nominal grating structures in said layer of photoresist.

22. The method of claim 20, wherein modifying at least one parameter of a photolithography process used to form a patterned layer of photoresist on at least one subsequently processed wafer comprises modifying at least one of a stepper exposure dose, a stepper focus, and a duration of a photoresist development process.

23. The method of claim 20, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming at least one sub-nominal grating structure in said layer of photoresist above a scribe line of said wafer.

24. The method of claim 20, wherein said photoresist features comprising said formed sub-nominal grating structure are comprised of lines or trenches.

25. The method of claim 20, further comprising forming said at least one sub-nominal grating structure in said layer of photoresist such that said plurality of photoresist features of said sub-nominal grating structure have a spacing that is less than a spacing of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

26. The method of claim 20, wherein forming a process layer comprises forming a process layer comprised of at least one of a metal, polysilicon and an insulating material having a dielectric constant less than 5.0.

27. The method of claim 20, wherein forming a layer of photoresist above said process layer comprises forming a layer of positive or negative photoresist above said process layer.

28. A method, comprising:

providing a library of optical characteristic traces, each of which corresponds to a sub-nominal grating structure comprised of a plurality of photoresist features having a known degree of residual photoresist material positioned between said photoresist features;

forming a process layer above a semiconducting substrate;

forming a layer of photoresist above said process layer;

forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features that have a spacing that is less than a spacing of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device;

illuminating said formed sub-nominal grating structure;

measuring light reflected off of said formed sub-nominal grating structure to generate an optical characteristic trace for said formed sub-nominal grating structure;

determining the presence of residual photoresist material between said features of said formed sub-nominal grating structure by comparing said generated optical characteristic trace to at least one optical characteristic trace from said library; and

modifying at least one parameter of a photolithography process used to form a patterned layer of photoresist on at least one subsequently processed wafer based upon said determined presence of residual photoresist material between said photoresist features of said sub-nominal grating structure.

29. The method of claim 28, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming a plurality of sub-nominal grating structures in said layer of photoresist.

30. The method of claim 28, wherein modifying at least one parameter of a photolithography process used to form a patterned layer of photoresist on at least one subsequently processed wafer comprises modifying at least one of a stepper exposure dose, a stepper focus, and a duration of a photoresist development process.

31. The method of claim 28, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming at least one sub-nominal grating structure in said layer of photoresist above a scribe line of said wafer.

32. The method of claim 28, wherein said photoresist features comprising said formed sub-nominal grating structure are comprised of lines or trenches.

33. The method of claim 28, further comprising forming said at least one sub-nominal grating structure in said layer of photoresist such that said plurality of photoresist features of said sub-nominal grating structure have a critical dimension that is less than a critical dimension of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

34. The method of claim 28, wherein forming a process layer comprises forming a process layer comprised of at least one of a metal, polysilicon and an insulating material having a dielectric constant less than 5.0.

35. The method of claim 28, wherein forming a layer of photoresist above said process layer comprises forming a layer of positive or negative photoresist above said process layer.

36. A method, comprising:

providing a library of optical characteristic traces, each of which corresponds to a sub-nominal grating structure comprised of a plurality of photoresist features having a known degree of residual photoresist material positioned between said photoresist features;

forming a process layer above a semiconducting substrate;

forming a layer of photoresist above said process layer;

forming at least one sub-nominal grating structure in said layer of photoresist above a scribe line of a wafer, said sub-nominal grating structure being comprised of a plurality of photoresist features;

illuminating said formed sub-nominal grating structure;

measuring light reflected off of said formed sub-nominal grating structure to generate an optical characteristic trace for said formed sub-nominal grating structure;

determining the presence of residual photoresist material between said features of said formed sub-nominal grating structure by comparing said generated optical characteristic trace to at least one optical characteristic trace from said library; and

modifying at least one parameter of a photolithography process used to form a patterned layer of photoresist on at least one subsequently processed wafer based upon said determined presence of residual photoresist material between said photoresist features of said sub-nominal grating structure.

37. The method of claim 36, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming a plurality of sub-nominal grating structures in said layer of photoresist, each of which are formed above a scribe line of a wafer.

38. The method of claim 36, wherein modifying at least one parameter of a photolithography process used to form a patterned layer of photoresist on at least one subsequently processed wafer comprises modifying at least one of a stepper exposure dose, a stepper focus, and a duration of a photoresist development process.

39. The method of claim 36, wherein said photoresist features comprising said formed sub-nominal grating structure are comprised of lines or trenches.

40. The method of claim 36, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a critical dimension that is less than a critical dimension of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

41. The method of claim 36, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a spacing that is less than a spacing of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

42. The method of claim 36, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a critical dimension and a spacing that is less than a critical dimension and a spacing of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

43. The method of claim 36, wherein forming a process layer comprises forming a process layer comprised of at least one of a metal, polysilicon and an insulating material having a dielectric constant less than 5.0.

44. The method of claim 36, wherein forming a layer of photoresist above said process layer comprises forming a layer of positive or negative photoresist above said process layer.

45. A method, comprising:

providing a wafer having at least one process layer and a layer of photoresist formed thereabove;

forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features;

illuminating said formed sub-nominal grating structure;

measuring light reflected off of said formed sub-nominal grating structure to generate an optical characteristic trace for said formed sub-nominal grating structure;

comparing the generated optical characteristic trace for said formed sub-nominal grating structure to a target optical characteristic trace; and

determining, based upon a comparison of said generated optical characteristic trace and said target optical characteristic trace, the presence of residual photoresist material between said features of said formed sub-nominal grating structure.

46. The method of claim 45, wherein providing a wafer having at least one process layer and a layer of photoresist formed thereabove comprises providing a wafer having at least one process layer and a layer of photoresist formed thereabove, said layer of photoresist being comprised of either a negative or positive photoresist material.

47. The method of claim 45, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming at least one sub-nominal grating structure in said layer of photoresist above a scribe line of said wafer.

48. The method of claim 45, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming a plurality of sub-nominal grating structures in said layer of photoresist.

49. The method of claim 45, further comprising modifying, based upon a comparison of said generated optical characteristic trace and said target optical characteristic trace, at least one parameter of a photolithography process used to form a patterned layer of photoresist on a subsequently processed wafer.

50. The method of claim 49, wherein modifying at least one parameter of a photolithography process used to form a layer of photoresist on at least one subsequently processed wafer comprises modifying at least one of a stepper exposure dose, a stepper focus, and a duration of a photoresist development process.

51. The method of claim 45, wherein measuring the reflected light comprises measuring the intensity of the reflected light.

52. The method of claim 45, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a critical dimension that is less than a critical dimension of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

53. The method of claim 45, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a spacing that is less than a spacing of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

54. The method of claim 45, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a critical dimension and a spacing that is less than a critical dimension and a spacing of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

55. The method of claim 45, wherein forming a process layer comprises forming a process layer comprised of at least one of a metal, polysilicon and an insulating material having a dielectric constant less than 5.0.

56. The method of claim 45, wherein forming a layer of photoresist above said process layer comprises forming a layer of positive or negative photoresist above said process layer.

57. A method, comprising:

providing a wafer having at least one process layer and a layer of photoresist formed thereabove;

forming at least one sub-nominal grating structure in said layer of photoresist above a scribe line of said wafer, said sub-nominal grating structure being comprised of a plurality of photoresist features;

illuminating said formed sub-nominal grating structure;

measuring light reflected off of said formed sub-nominal grating structure to generate an optical characteristic trace for said formed sub-nominal grating structure;

comparing the generated optical characteristic trace for said formed sub-nominal grating structure to a target optical characteristic trace; and

modifying, based upon a comparison of said generated optical characteristic trace and said target optical characteristic trace, at least one parameter of a photolithography process used to form a patterned layer of photoresist on a subsequently processed wafer.

58. The method of claim 57, wherein providing a wafer having at least one process layer and a layer of photoresist formed thereabove comprises providing a wafer having at least one process layer and a layer of photoresist formed thereabove, said layer of photoresist being comprised of either a negative or positive photoresist material.

59. The method of claim 57, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming a plurality of sub-nominal grating structures in said layer of photoresist.

60. The method of claim 57, wherein modifying at least one parameter of a photolithography process used to form a layer of photoresist on at least one subsequently processed wafer comprises modifying at least one of a stepper exposure dose, a stepper focus, and a duration of a photoresist development process.

61. The method of claim 57, wherein measuring the reflected light comprises measuring the intensity of the reflected light.

62. The method of claim 57, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a critical dimension that is less than a critical dimension of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

63. The method of claim 57, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a spacing that is less than a spacing of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

64. The method of claim 57, wherein forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features, comprises forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features having a critical dimension and a spacing that is less than a critical dimension and a spacing of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

65. The method of claim 57, wherein forming a process layer comprises forming a process layer comprised of at least one of a metal, polysilicon and an insulating material having a dielectric constant less than 5.0.

66. The method of claim 57, wherein forming a layer of photoresist above said process layer comprises forming a layer of positive or negative photoresist above said process layer.

67. A method, comprising:

providing a wafer having at least one process layer and a layer of photoresist formed thereabove;

forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features that have a critical dimension that is less than a critical dimension of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device;

illuminating said formed sub-nominal grating structure;

measuring light reflected off of said formed sub-nominal grating structure to generate an optical characteristic trace for said formed sub-nominal grating structure;

comparing the generated optical characteristic trace for said formed sub-nominal grating structure to a target optical characteristic trace;

determining, based upon a comparison of said generated optical characteristic trace and said target optical characteristic trace, the presence of residual photoresist material between said features of said sub-nominal grating structure; and

modifying, based upon a comparison of said generated optical characteristic trace and said target optical characteristic trace, at least one parameter of a photolithography process used to form a patterned layer of photoresist on a subsequently processed wafer.

68. The method of claim 67, wherein providing a wafer having at least one process layer and a layer of photoresist formed thereabove comprises providing a wafer having at least one process layer and a layer of photoresist formed thereabove, said layer of photoresist being comprised of either a negative or positive photoresist material.

69. The method of claim 67, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming at least one sub-nominal grating structure in said layer of photoresist above a scribe line of said wafer.

70. The method of claim 67, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming a plurality of sub-nominal grating structures in said layer of photoresist.

71. The method of claim 67, wherein modifying at least one parameter of a photolithography process used to form a layer of photoresist on at least one subsequently processed wafer comprises modifying at least one of a stepper exposure dose, a stepper focus, and a duration of a photoresist development process.

72. The method of claim 67, wherein measuring the reflected light comprises measuring the intensity of the reflected light.

73. The method of claim 67, further comprising forming said at least one sub-nominal grating structure in said layer of photoresist such that said plurality of photoresist features have a spacing that is less than a spacing of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

74. The method of claim 67, wherein forming a process layer comprises forming a process layer comprised of at least one of a metal, polysilicon and an insulating material having a dielectric constant less than 5.0.

75. The method of claim 67, wherein forming a layer of photoresist above said process layer comprises forming a layer of positive or negative photoresist above said process layer.

76. A method, comprising:

providing a wafer having at least one process layer and a layer of photoresist formed thereabove;

forming at least one sub-nominal grating structure in said layer of photoresist, said sub-nominal grating structure being comprised of a plurality of photoresist features that have a spacing that is less than a spacing of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device;

illuminating said formed sub-nominal grating structure;

measuring light reflected off of said formed sub-nominal grating structure to generate an optical characteristic trace for said formed sub-nominal grating structure;

comparing the generated optical characteristic trace for said formed sub-nominal grating structure to a target optical characteristic trace;

determining, based upon a comparison of said generated optical characteristic trace and said target optical characteristic trace, the presence of residual photoresist material between said features of said sub-nominal grating structure; and

modifying, based upon a comparison of said generated optical characteristic trace and said target optical characteristic trace, at least one parameter of a photolithography process used to form a patterned layer of photoresist on a subsequently processed wafer.

77. The method of claim 76, wherein providing a wafer having at least one process layer and a layer of photoresist formed thereabove comprises providing a wafer having at least one process layer and a layer of photoresist formed thereabove, said layer of photoresist being comprised of either a negative or positive photoresist material.

78. The method of claim 76, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming at least one sub-nominal grating structure in said layer of photoresist above a scribe line of said wafer.

79. The method of claim 76, wherein forming at least one sub-nominal grating structure in said layer of photoresist comprises forming a plurality of sub-nominal grating structures in said layer of photoresist.

80. The method of claim 76, wherein modifying at least one parameter of a photolithography process used to form a layer of photoresist on at least one subsequently processed wafer comprises modifying at least one of a stepper exposure dose, a stepper focus, and a duration of a photoresist development process.

81. The method of claim 76, wherein measuring the reflected light comprises measuring the intensity of the reflected light.

82. The method of claim 76, further comprising forming said at least one sub-nominal grating structure in said layer of photoresist such that said plurality of photoresist features have a critical dimension that is less than a critical dimension of additional photoresist features formed in said layer of photoresist, said additional photoresist features to be used as a mask in etching production features in an integrated circuit device.

83. The method of claim 76, wherein forming a process layer comprises forming a process layer comprised of at least one of a metal, polysilicon and an insulating material having a dielectric constant less than 5.0.

84. The method of claim 77, wherein forming a layer of photoresist above said process layer comprises forming a layer of positive or negative photoresist above said process layer.